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Area Forecast Discussion (AFD)

Issued by Pendleton, OR (PDT)

FXUS66 KPDT 250332

Area Forecast Discussion
National Weather Service Pendleton OR
832 PM PDT Mon Jun 24 2019

.UPDATE...The flow aloft is now shifting to be from the southwest
as an upper low pressure system moves southward over the northeast
Pacific and the Gulf of Alaska. The southwest flow will become
more pronounced on Tuesday and Wednesday with moisture and
instability increasing into the region in the SW flow. The
combination of this moisture and instability with surface heating
will lead to showers and afternoon thunderstorms mainly over the
mountains on Tuesday and in all areas on Wednesday. This system
looks to contain some decent amounts of moisture and therefore
there could be some heavy rain with some showers and
thunderstorms. Thus the fire weather threat, at this time, is not
too high, but will need to watch that closely, especially if there
are abundant lightning strikes over the driest areas such as the
lower elevations including the Lower Columbia Basin and adjacent
low lands. In the mountains, fine vegetation is still fairly 
green and not yet completely cured yet. The best day for 
thunderstorms and heavy rain will be on Wednesday as the upper low
moves into the Pacific Northwest during the day and the south to 
southwest flow ahead of it is the strongest. Then after that an 
upper trough will linger over the west for the rest of the week 
with unsettled, cool, and showery conditions (cool for the time 
of year with below normal temperatures). Current forecast looks 
good and forecast updates will not be needed this evening. 88


.AVIATION...06Z TAFs...There will be widespread high clouds and
some mid clouds as the flow aloft turns southwesterly. This will
help to keep temperatures up tonight as the cirrus is rather
thick. There will also be increasing mid level clouds between
060-100. However, conditions will remain VFR overnight at all TAF
locations. On Tuesday, there could be some showers and 
thunderstorms over KRDM and KBDN, which could drop to MVFR for 
brief times...otherwise conditions will remain VFR elsewhere. 
Winds will be mostly light through the next 24 hours and mostly 
less than 10 kts. 88


.PREV DISCUSSION... /issued 431 PM PDT Mon Jun 24 2019/ 

SHORT TERM...Tonight through Thursday...A closed upper level low
pressure system off the west coast of Canada will drop south and 
take up a position just off the Pacific Northwest coast on Tuesday. 
This will turn our current westerly flow to southwesterly and 
introduce some atmospheric instability that will translate into 
showers and potential thunderstorms Tuesday afternoon and overnight. 
By Wednesday the low will be along the Oregon coast and our flow 
will be more southerly with even better instability and moisture 
leading to more widespread showers and thunderstorms by afternoon 
and overnight. Some of these showers and thunderstorms could produce 
some brief heavy rainfall. On Thursday the low moves onshore and 
begins to usher in cooler air and shift the better instability to 
the east of the forecast. Still, there will be showers and some 
thunderstorm potential but not as great as on Wednesday and mainly 
over the eastern mountains.  

LONG TERM...Thursday Night through Monday...Thursday night a trough 
will remain over the area with its central upper low on the west 
side of the Cascades. After thunderstorms end in the evening, a 
slight chance of showers will continue over the mountains and 
central Oregon through Friday morning. Friday afternoon, the low 
will be weakening and beginning to move northeast. A slight chance 
to chance of showers will continue in the mountains and central 
Oregon with the rest of the area dry. A slight chance of afternoon 
and evening thunderstorms will be confined to the Ochoco-John Day 
Highlands and from the Blue Mountains eastward. Friday night the low 
will lift into British Columbia with a shallow trough lingering over 
the area. Showers will taper off in the evening. Saturday through 
Sunday will see the trough remaining but do not see much in the way 
of moisture or disturbances so have a dry forecast. Sunday night and 
Monday models diverge with the GFS and Canadian having a ridge over 
us while the ECMWF has a weak low and trough over the area. Have 
leaned towards the GFS/Canadian solutions and have kept the forecast 
dry. Temperatures will be in a warning trend through the period. 
Friday will be cool and below normal with highs in the 70s with 60s 
in the mountains. Temperatures will then warm 3-5 degrees each day 
ending up in the mid 80s to lower 90s with mid 70s to lower 80s in 
the mountains next Monday. Perry


PDT  52  80  54  76 /   0  10  20  40 
ALW  55  82  57  79 /   0  10  20  40 
PSC  55  85  58  80 /   0   0  20  20 
YKM  51  80  54  75 /   0  10  20  40 
HRI  55  83  57  80 /   0   0  20  30 
ELN  49  76  51  71 /   0  10  20  60 
RDM  44  75  47  69 /   0  20  30  60 
LGD  48  76  50  76 /   0  30  30  60 
GCD  48  76  49  75 /   0  20  30  50 
DLS  55  79  57  72 /   0  10  20  40